The invention relates to a multiband antenna, typically for receiving Global Positioning System (GPS) signals.
Conventional two arm frequency independent Archimedean spiral antennas used to receive GPS L1/L2 signals exhibit poor group delay (d/df) variation performance over the hemispherical coverage required, and low efficiency. The variation rises from the movement of the active radiating region over the bandwidth of the GPS signal, multiple regions radiating beyond the primary region, and the use of only two ports. This variation degrades the performance of the system, requiring corrections in software to offset the variation. The variation is also undesirable in GPS surveying applications where low group delay variation is critical to obtain extremely accurate GPS locations. Low efficiency causes difficulty in acquiring low angle satellite signals and arises from the balun assembly needed to feed the two spiral ports, and current losses in the arms before reaching the radiating region.
WO 01/13465 (Kunysz) discloses an aperture coupled slot array antenna. Energy is coupled into each slotted opening by a transmission line in the shape of a circular arc. An impedance load is coupled to a terminal end of the transmission line to provide a leaky-wave antenna configuration and to thus ensure a uniform amplitude coupling to all slotted openings.
U.S. Pat. No. 3,949,407 (Jagdmann) discloses a spiral antenna in which the outer ends of the spiral arms are direct fed by a hybrid feed network. A multi-band antenna is disclosed with interleaved sets of low frequency and high frequency slotted openings.
U.S. Pat. No. 6,181,277 (Kesler) discloses a dual frequency microstrip patch antenna. A top microstrip patch element is separated from the ground plane by a larger second microstrip patch element. The top microstrip patch element is driven by a feed network consisting of three hybrid couplers.
U.S. Pat. No. 5,621,422 (Wang) discloses a two arm spiral-mode microstrip antenna in which the spiral arms are driven by a hybrid circuit with either 0 degree or 180 degree phase shift between the two arms.
U.S. Pat. No. 5,838,282 (Lalezari) discloses a multi-frequency antenna in which high frequency and low frequency radiating elements are each driven by respective feed circuits. A stacked patch antenna operates in a first frequency band and a crossed dipole element operates in a second frequency band.
U.S. Pat. No. 3,039,099 (Chait) discloses a linearly polarized spiral antenna system. Two spiral arms are coupled at both ends to a drive circuit.
U.S. Pat. No. 6,166,694 (Ying) discloses a printed twin spiral dual band antenna. A single (relatively long) low frequency spiral arm and a single (relatively small) high frequency spiral arm are coupled with a feeding pin, matching bridge, loading resistor and grounded post.
U.S. Pat. No. 3,925,784 (Phelan) discloses a 4-arm spiral antenna with inner ends coupled to a network of diodes, and outer ends coupled to switches.
U.S. Pat. No. 5,300,936 (Izadian) discloses a multiple band antenna, including one embodiment (FIG. 8) in which an array of four longitudinal radiating elements form two orthogonal dipole pairs. Hybrid circuits provide output signals in response to illumination of the dipole pairs.
U.S. Pat. No. 4,912,481 (Mace) discloses a multi-frequency antenna array in which an array of patches operable at high frequencies define a rectangular grid which is operable at low frequencies.
The paper E. Gschwendtner, W. Wiesebeck, xe2x80x9cLow-Cost Spiral Antenna with Dual-Mode Radiation Pattern for Integrated Radio Servicesxe2x80x9d, available at www.comcar.de/papers/ap2000.pdf describes a four arm spiral antenna with a coplanar waveguide transmission line connected to the centre of the spiral.
U.S. Pat. No. 5,541,617 (Connolly) discloses a quadrifilar helix antenna in which a 180 hybrid circuit drives the four radiating elements.
U.S. Pat. No. 5,955,997 (Ho) discloses a microstrip-fed cylindrical slot antenna. The antenna is driven by a non-isolating inline power splitter with an excess quarter-wavelength line in one output arm which generates the required 90 degrees phase differentials between the radiating slots.
U.S. Pat. No. 6,201,513 (Ow) discloses a two-arm spiral antenna driven by a two port balun assembly.
It is an object of the invention to provide an alternative antenna and feed network configuration with improved characteristics, or at least to provide a useful alternative.
A first aspect of the exemplary embodiment provides a multi-band antenna comprising two or more low frequency radiators dimensioned to operate in a low frequency band; two or more high frequency radiators dimensioned to operate in a high frequency band, each high frequency radiator being substantially coplanar with the low frequency radiators; and a hybrid feed network having two or more antenna ports, each antenna port being coupled with one or more of the radiators.
A second aspect of the exemplary embodiment provides a multi-band antenna comprising two or more low frequency radiators dimensioned to operate in a low frequency band; two or more high frequency radiators dimensioned to operate in a high frequency band; and a feed network having two or more antenna ports, wherein each antenna port is coupled with a low frequency radiator and a high frequency radiator.